Experimental study on physical and mechanical properties of ultra-high performance concrete with recycled coarse aggregate and steel fiber under high temperature
At present,the research on the performance of concrete with recycled coarse aggregate and fiber is relatively suffi-cient,but the understanding on its performance changes after high temperature treatment is insufficient.To this end,three types of concrete,namely ultra-high performance concrete(UHPC),50%recycled coarse aggregate UHPC(50%R-UHPC),and 50%recycled coarse aggregate-1.0%steel fiber UHPC(50R-1.0%S-UHPC),were treated under high temperature(200℃,400℃,600℃,800℃).Then the mechanical properties of the concretes,including uniaxial compressive strength,elastic modulus,splitting tensile strength,and flexural strength,as well as impermeability and thermal conductivity were studied.The results indi-cate that the addition of recycled coarse aggregate to the concrete weakens its mechanical properties,impermeability,and thermal conductivity,resulting in a decline in compressive,tensile,and flexural strength,as well as an increase in porosity and permeabili-ty.However,the addition of steel fibers enhances the mechanical properties and thermal conductivity of the concrete,but also re-sults in an increase in porosity and permeability.High temperature treatment weakens the concrete mechanical properties,imper-meability,and thermal conductivity,and there is a threshold temperature of 400℃.Prior to 400℃,the impact of high temperature treatment on these properties is minimal,but once the threshold is exceeded,the properties weaken rapidly.With respect to both UHPC and 50%R-UHPC,the differences in mechanical properties and thermal conductivity gradually diminish with the increase of the treatment temperature.
ultra-high performance concreterecycled aggregate concretesteel fiberhigh temperature treatmentmechan-ics propertiesimpermeabilitythermal conductivityempirical prediction model
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